faithless

/F EY1 TH L AH0 S/
adjective
  1. 1

    Lacking faith; lacking belief in something.

  2. 2

    Not believing in God, religion, or a comparable ideology.

  3. 3

    Unfaithful (said of people, towards their partners)

  4. 4

    Not observant of promises or covenants.

  5. 5

    Not true to allegiance, duty, or vows

  6. 6

    Serving to disappoint or deceive

Source: https://en.wiktionary.org/wiki/faithless